The advantages of a gas filled sole are well known and are discussed in some detail in a number of patents, such as the discussions in U.S. Pat. Nos. 4,887,367 and 4,936,029. Soles filled with gasses provide shock absorption and resiliency superior to that achievable with material soles. The choice of gas or gas mixtures used in soles affects not only the final weight of the footwear but also the degree of resiliency and elasticity and the useful life of the sole. Because of its light weight, helium is an optimum choice of gas for use in soles, particularly for use in athletic shoes in which any decrease in shoe weight may aid in running and jumping.
Recent attempts to use helium in soles of athletic shoes, however, have been unsuccessful as helium is the second lightest gas and is comprised of small atoms which easily diffuse through the materials used to construct the soles and helium bladders therein. The result of these prior efforts is a deflated shoe sole which does not provide the lift and support obtained from a filled helium sole. Other athletic shoe manufacturers have used heavier gasses to inflate shoe soles. Such soles, however, are heavier than those of the present invention and do not provide the degree of lift and elasticity obtainable with the soles of the present invention.
Despite the need for resilient and lightweight footwear, the sole of the shoe or sandal must also provide sufficient support to the foot and must be sufficiently durable to provide an acceptable service life. Furthermore, it is advantageous for the amount of support and resilience provided by the sole to different areas of the foot to vary as the stride of the wearer progresses. That is, in walking, jogging or running, the area of the foot in contact with the ground rotates from the heel to the ball of the foot. Therefore, it is well known to permit the gas to flow into and out of connecting chambers underlying the ball and the heel of the foot. Because of the light weight of helium, as the gas moves between the chambers, the sole imparts a lift to the foot and facilitates the natural roll of the stride.
The present invention is an improvement to the invention disclosed and claimed in U.S. Pat. No. 6,009,637, issued on Jan. 4, 2000 and entitled "Helium Footwear Sole." The '637 patent describes a sole comprised of a silicone midsole having core modules filled with helium. One of the difficulties associated with the type of helium filled soles described in the '637 patent is the propensity of the helium to diffuse through the materials of the midsole and escaping into or through the top sole or bottom sole. The present invention addresses this problem and provides a sole which impedes such diffusion of the helium resulting in a sole which contains the helium for the useful life of the footwear.
Great amounts of pressure can be generated on the foot during any kind of ambulation, including walking, jogging and running. Footwear manufacturers and designers attempt to ameliorate the discomfort of the foot pressing against a hard sole by using softer materials to construct either the sole or as a padding on top of the soles of footwear. Soles comprised of a soft material are generally not as durable as soles made of rigid or semi-rigid materials. Insole padding materials have a tendency to flatten and compress with use thereby decreasing the cushioning provided to the foot. Yet other manufacturers offer gel-filled insoles which can be purchased separately from the footwear and moved from shoe to shoe. Such movable insoles, however, take up space inside the shoe and can result in discomfort on the top of the foot. There is a need, therefore, for a sole which cushions the foot during the standard service life of footwear but yet which provides support and durability.